EERE Network News - 12/12/07

The key to making use of the untapped geothermal energy resources that lie beneath our feet is to improve the technologies used to discover and tap into those resources, according to a recent report from the Geothermal Energy Association (GEA). The industry group estimates that hundreds of thousands of megawatts of geothermal power lie beneath the surface in the United States, waiting for new exploration tools, better resource characterization techniques, lower-cost drilling technologies, and improved tools to predict the behavior of geothermal reservoirs. The GEA's new report describes the techniques used to find and exploit geothermal reservoirs and fleshes out those techniques with specific case studies, providing a useful overview of the technologies employed by the geothermal energy industry and the challenges the industry faces.

The report also calls for building a test facility to try out the concepts of so-called Enhanced Geothermal Systems (EGS), in which geothermal resources are modified to enhance their energy production. For instance, an EGS system could involve injecting high-pressure water into hot, dry rocks located deep underground, or it could employ a similar technique to expand an existing reservoir of geothermal hot water.

One example of the new exploration technology called for in the GEA report is provided by DOE's Lawrence Berkeley National Laboratory (LBNL). Geochemists at LBNL and Arizona State University studied fluid samples from wells, springs, and steam vents and found that some fluids have a high proportion of the helium-three isotope. Helium-three is thought to be left over from the formation of the solar system and is retained in high proportions within Earth's mantle, but the crust is higher in radioactive elements that decay to form helium-four, so a high ratio of helium-three to helium-four is indicative of material from the mantle. In non-volcanic regions, high helium-three ratios could indicate the flow of surface fluids through deep fractures that penetrate the crust, conditions that should also create geothermal reservoirs. Surveying geothermal fluids across the northern Basin and Range, which spans across parts of California, Idaho, Nevada, Oregon, and Utah, the researchers found a general east-west trend in helium ratios, but also found some anomalous high proportions of helium-three that may indicate underlying geothermal resources.